WASHINGTON — Congressional Democrats are holding their ground in opposition to President Trump’s proposed border wall after Trump threatened to ‘‘close down the government’’ if lawmakers do not provide money for the project when they return from August recess.

On Wednesday, Senate minority leader Charles Schumer of New York and House minority leader Nancy Pelosi of California repeated their objections to funding a wall, and argued Trump would be responsible if the government shuts down over the impasse.

‘‘If the president pursues this path, against the wishes of both Republicans and Democrats, as well as the majority of the American people, he will be heading towards a government shutdown which nobody will like and which won’t accomplish anything,’’ Schumer said in a statement.

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Trump’s threat Tuesday night during a campaign-style rally in Phoenix instantly raised the stakes for the showdown over government spending that awaits lawmakers. Federal spending authority expires in a little more than a month, requiring Congress to act to keep the government fully operating past Sept. 30.

Many Republicans are hoping to include border wall funding in any deal to keep the government open, and key conservative lawmakers have rallied to Trump’s side. But Democrats on Wednesday showed no sign of backing down.

‘‘Last night, President Trump yet again threatened to cause chaos in the lives of millions of Americans if he doesn’t get his way,’’ Pelosi said in a statement. ‘‘Make no mistake: The President said he will purposefully hurt American communities to force American taxpayers to fund an immoral, ineffective and expensive border wall.’’

Trump, escalating a conflict that has been brewing for months, told supporters Tuesday night: ‘‘Believe me, if we have to close down our government, we’re building that wall. Let me be very clear to Democrats in Congress who oppose a border wall and stand in the way of border security: You are putting all of America’s safety at risk.’’

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Neither Republican Senate majority leader Mitch McConnell of Kentucky nor Republican House Speaker Paul Ryan of Wisconsin has weighed in on Trump’s remarks, but some prominent conservative lawmakers are urging Republicans to support the president.

‘‘Congress would do well to join the President by keeping our own commitments and including border wall funding in upcoming spending measures,’’ Freedom Caucus Chairman Representative Mark Meadows a North Carolina Republican, wrote on Twitter before Tuesday’s rally.

Rasmussen Reports, a Republican firm, conducted a poll of likely US voters late last month and found that a solid majority of Americans oppose building a border wall, with 37 percent supporting Trump’s proposal versus 56 percent against. That is largely unchanged from a poll conducted in February by the nonpartisan Pew Research Center that found Americans opposed the wall 62 percent to 35 percent.

House Republicans voted last month to provide $1.6 billion in seed funding for the border wall as part of a larger spending package. That bill is expected to be taken up in the Senate, where Democrats can filibuster any measure that funds the wall or includes other GOP provisions that they have termed ‘‘poison pills.’’

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A 2017 spending bill passed into law earlier this year did not include border wall funding after Democrats refused to accept it. That impasse increased pressure on Republicans to deliver wall funding in a future spending battle.

Representative Nita Lowey of New York, the top Democrat on the House Appropriations Committee, called Trump’s threat the ‘‘polar opposite of leadership’’ and said the president should be held accountable if the government shuts down.

‘‘Wasting tens of billions on a useless and immoral border wall is a nonstarter for Democrats, particularly at a time of such real need in our communities. Congress should use this funding to help American families — not fulfill campaign applause lines,’’ Lowey said Wednesday in a statement.

Rank-and-file Democrats and several caucuses representing them took to Twitter Tuesday to double down on that position.

‘‘Threatening to shut down the gov’t for a campaign promise and a wall we don’t need is irresponsible and reckless,’’ Representative Bennie Thompson of Mississippi, the top Democrat on the House Homeland Security Committee, tweeted from an account representing the panel’s Democrats.

Tweeted the Congressional Hispanic Caucus: ‘‘Trump irresponsibly vows to shut down govt if his immoral, ineffective & unnecessary #borderwall isn’t funded by the American taxpayer.’’